Questions on tcp_send

[Steven Mickovski]

hello,
i have some problems understanding the tcp_send routine in 
net/ipv4/tcp.c:

1)
 if (skb_tailroom(skb) > 0) {
                                /* We have some space in skb 
head.
				Superb! */
                                ...
				...
                        } else {
                                int merge = 0;
                                int i = 
skb_shinfo(skb)->nr_frags;
                                struct page *page = 
TCP_PAGE(sk);
                                int off = TCP_OFF(sk);
				if (can_coalesce(skb, i, page, off) && off != PAGE_SIZE) 
{merge=1;}

My understanding of the skb_tailroom condition is that it's for 
the
case when the previous sk_buff can accomodate the new buffer to 
be
sent, and it checks if this can be done in the space allocated to 
it,
or if it should stuff it into the page where the space is 
allocated.

Is this correct?

2) If so, then why does "can_coalesce" check if:
  (page == frag->page && off == frag->page_offset+frag->size)
   to decide if the data can be merged with that in the 
previous
    sk_buff?

Thanks in advance! Help appreciated...

Steve
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